<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Hello</title>
    <script>
        alert("Hello world!")
    </script>
    <!--外部引入, 这个标签必须是双标签-->
    <script src="js/qj.js"></script>
</head>
<body>
</body>
</html>